Director Burgess Clark is working with a group of young actors in a nondescript studio at the Huntington Avenue YMCA. “Stop!” he says, pausing for dramatic effect. The actors have just rehearsed a musical number that’s meant to be high-spirited, practicing choreography that is new to them. “Is that happy?” he asks them. “You need to sell it to the back row!”

They take it from the top. Soprano Adena Walker belts out the tune with excitement. And emotion. Her delivery is the vocal equivalent of an exclamation point.

Judging from the energy level in the room, these actors could be singing about conquering the world. Instead, the upbeat subject is, well, grammar. As in interjections, like “hey” and “eek” — the kind of little word that “starts a sentence right.” The song “Interjections!,” of course, is a classic from “Schoolhouse Rock!,” the series of educational cartoons that originally aired on Saturday mornings in the 1970s and ’80s. The Boston Children’s Theatre production of the stage adaptation opens April 19 in the Roberts Studio Theatre at the Boston Center for the Arts.

Walker, 24, is too young to have seen the animated shorts when they first appeared, but she is a devotee of the ditties nonetheless. In fact, she adores children’s programming from the ’70s. The ringtone on her cellphone is the title track from “Free to Be . . . You and Me,” a feel-good TV special from that era. And Fred Rogers, the neighborly television icon, is her idol. “I was born at the wrong time,’’ says the Brookline native. “I watched a ‘Mister Rogers’ clip the other day, and I cried. He was saying that there is a child in all of us. I love that.”

The stage version of “Schoolhouse Rock!” is framed around a new teacher who is nervous about meeting his first class. A group of characters representing different parts of his personality emerge to give him a pep talk, singing hits from the Emmy Award-winning series. Six actors, ranging in age from 13 to 24, perform such standbys as “I’m Just a Bill,” “Three Is a Magic Number,” and “Conjunction Junction.”

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The iconic tunes, penned by Bob Dorough, Lynn Ahrens, David Frishberg, and others, are instantly recognizable to Generation Xers who grew up eating their Cap’n Crunch in front of the small screen on Saturday mornings. That familiarity isn’t lost on Clark, the company’s executive artistic director. “All these songs are indelibly printed on the minds of so many adults and children today,’’ he says. “The other day I was in a car full of people my age, which is 51. Someone started singing ‘Just a Bill,’ and everybody chimed in. It’s a little startling to me that 40 years later people talk about this piece with such affection.”

The challenge for Clark and his team is to make the songs just as vibrant and appealing to folks who can recite all the words as to those who may be hearing them for the first time. “This piece exists in our collective consciousness, and that can be a little daunting,’’ Clark says. “You have to meet people at the door with their expectations and exceed them. It’s about making the experience live. We’re not reinventing, but refocusing.”

Clark also has another mission as a director, one he brings to all his shows at the children’s theater. He says he aims to give his young performers perspective about life in the theater. During rehearsal, he spins yarns about various productions he has directed, including a tale about an actor who carried on a death scene for far too long. “I said, ‘When he stabs you, I want you to exit screaming.’ That was my mistake. He would die center stage and resurrect himself, drowning in chiffon and screaming all the way out.”

“Schoolhouse Rock!” ensemble member Colin Budzyna, 16, has been working with Clark for several years. He isn’t a rabid fan of the old cartoons, but he has heard the numbers around the house since he was just a tot. “It’s not my generation, but my parents love it,’’ the Newburyport High School sophomore says with a slight smile. “My parents can sing every word to every song. When I found out I was cast, my mom started singing ‘Conjunction Junction.’ ’’

The original show, which featured whimsical elements like speech bubbles and a singing scrap of paper, is cartoony by definition. The actors need to play it big. “The great thing I found out about children’s theater is that most of the time it’s way crazy and over the top,’’ Budzyna says. “It makes you feel like an idiot when you’re doing it in rehearsal, but when you get onstage, it is so much fun.’’

Walker, a classically trained singer, embraces the style. “The cartoony stuff is only cartoony if you let it be,’’ she says. “You know what you are doing is funny. If you think it is hilarious, you project that. You have to be 100 percent into it.”

Under Clark’s direction, Boston Children’s Theatre has done serious shows such as “The Diary of Anne Frank,” “To Kill a Mockingbird,” and “Reflections of a Rock Lobster,” the true story of a teenager who sued his school district for the right to bring his boyfriend to the prom. “Schoolhouse Rock!” is lighter fare — educational, to be sure, but full of whimsy. “It’s like having a day at the amusement park,” Clark says. “If you are an attorney, you enjoy doing the research, but you also enjoy a day at the park.”

That carnival atmosphere, circa the ’70s, is just what Walker loves. “Sometimes, I wish I was Mr. Rogers,’’ she says. During the day, Walker is a substitute teacher in Brookline and Boston. She doesn’t yell at her students, she says. She sings instead. “My main goal in life is to make kids feel special. I just want them to know that someone cares about them. That is what Mr. Rogers says.”

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